This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Plant cell wall polysaccharides are the most abundant organic molecules and play important roles in the quality of plant-based foods and have beneficial effects in human diets, and they are also the essential materials in industry as a source of fibers and renewable biofuel. Xyloglucan is the principal hemicellulosic polysaccharide in the primary cell walls of most plants. Xyloglucan xylosyltransferase (XXT) is membrane-associated enzyme and a key player in the biosynthesis of xyloglucans. It catalyzes xylosylation reaction and adds xylose onto beta-1,4-glucan backbone. Currently, little is known about the molecular mechanisms underlying the cell wall synthesis, particularly the polysaccharide biosynthesis. We are studying membrane-associated xyloglucan xylosyltransferase XXT2 from Arabidopsis. AtXXT2 protein was expressed and purified, and crystals were obtained recently. We will determine XXT crystal structures to reveal the unique structural features at the atomic level and dissect the reaction mechanism governing the xylosylation process and the cell wall biosynthesis. This structural study will also provide a structural guide for manipulation and engineering of cell wall composition to improve the quality of plants with important impacts in agriculture and industry (e.g., biofuel production) as well as food nutrition and human health.